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If a contractor recently told you your insulation is bad, you probably left that conversation with a spray foam quote and zero clarity on whether it was actually necessary. That confusion is common. The different home insulation types each have a sales pitch behind them, and almost nobody explains the actual cost-versus-savings math before asking you to sign something.
Spray foam is almost always the most expensive option on any quote, and almost always presented as the premium default. This guide gives you the numbers to evaluate that yourself: installed costs, R-value requirements, and a 10-year ROI comparison that no installer will hand you. If you haven’t yet confirmed where your home is actually losing heat, our home energy audit guide covers how to find out before committing to any material.
Quick answer: best insulation by situation
| Your situation | Best choice |
|---|---|
| Standard attic, hiring out | Blown-in cellulose |
| Standard attic, DIY | Fiberglass batts |
| Rim joists | Closed-cell spray foam |
| Crawl space walls | Closed-cell spray foam |
| Exterior walls (new construction) | Fiberglass or mineral wool batts |
Table of Contents
- What insulation actually does (and why type matters less than you think)
- The 5 home insulation types: what they are and where they go
- R-value explained: what number do you actually need?
- How much does home insulation cost?
- Attic Insulation Savings Calculator
- Spray foam vs. fiberglass insulation: the real money comparison
- Can you DIY? A realistic guide by type
- Does insulation actually reduce energy bills?
- How to choose: a decision framework by situation
- Frequently Asked Questions
What insulation actually does (and why type matters less than you think)
Insulation slows heat transfer. In winter, it keeps heat inside your house. In summer, it keeps heat out. The speed at which heat moves through a material is measured by its R-value — the higher the number, the slower the transfer, the better the insulation.
Here’s what most insulation articles won’t tell you: at the same R-value, any properly installed insulation type performs identically. R-30 fiberglass and R-30 cellulose and R-30 open-cell spray foam all resist heat transfer at the same rate. The material itself doesn’t determine performance. The R-value does. We’ve checked this against DOE’s insulation guidance, and the physics is unambiguous.
Key takeaway: Once any insulation type reaches the same R-value, it delivers the same annual energy savings. What differs — sometimes by a factor of five — is installed cost.
| Insulation type | R-value (attic, to R-49) | Annual energy savings |
|---|---|---|
| Fiberglass batts | R-49 | Same |
| Blown-in cellulose | R-49 | Same |
| Closed-cell spray foam | R-49 | Same |
| Same R-value = same energy savings. Type affects cost and installation method, not thermal performance. | ||
What actually separates good insulation jobs from poor ones isn’t material choice. It’s two things: hitting the target R-value for your climate, and sealing the air gaps before or alongside the insulation install. An attic with perfectly installed fiberglass batts but unsealed penetrations around pipes and light fixtures will lose more heat than a lower-R attic that’s been properly air sealed.
With that context, here’s how the main types compare.
The 5 home insulation types: what they are and where they go
These are the types you’ll encounter in contractor quotes and at home improvement stores. Understanding each one takes about two minutes and will immediately help you evaluate any bid you receive.
Fiberglass batts and rolls
The pink or yellow fluffy material you’ve seen in walls and attics. It comes in pre-cut widths sized to fit standard stud and joist spacing (16″ or 24″ on center). Batts are the most common insulation in U.S. homes by a wide margin.
Best for: Open attic floors, unfinished walls, floors over unconditioned spaces.
Weakness: Batts must fit snugly with no gaps or compression. A common mistake is compressing a batt to fit a shallower cavity — a 6-inch R-19 batt stuffed into a 5.5-inch space can lose 20 to 25 percent of its rated R-value. They don’t air-seal, so a separate air-sealing step is required for best results.
Blown-in insulation (fiberglass or cellulose)
Loose fill material blown in using a hose and machine. Fiberglass blown-in is similar to batts but in loose form. Cellulose is made from recycled newspaper treated with fire retardants and is slightly denser, with better air resistance.
Best for: Attic floors, especially retrofit jobs where you’re adding insulation on top of existing. Also good for hard-to-reach spaces and existing wall cavities (dense-pack cellulose).
Weakness: Cellulose can absorb moisture if vapor management is poor. It also settles about 15 to 20 percent over time, so installers intentionally blow it deeper than the final target depth. DOE R-value tables account for this. Both types require renting a blowing machine, though this is typically free at big-box stores with the purchase of enough bags.
Spray foam (open-cell and closed-cell)
A two-component liquid that expands and hardens on contact. Open-cell spray foam is softer, lighter, and less expensive, making it good for interior applications and sound dampening. Closed-cell is denser, has a much higher R-value per inch (6 to 7 versus roughly 3.7 for open-cell), and also acts as a vapor barrier.
Best for closed-cell: Crawl space walls, rim joists, cathedral ceilings, and tight cavities where you can’t get enough thickness for other types.
Best for open-cell: Interior walls for sound control, or attic roof decks where you want a conditioned attic (a less common application).
Weakness: Cost. Requires professional installation for anything beyond small-area gap filling. Closed-cell spray foam uses isocyanate compounds during application; these are respiratory irritants at exposure — occupants should leave during application and for 24 hours after, and the area needs ventilation. Improperly mixed foam can off-gas for far longer.
Rigid foam board
Solid panels of foam insulation, most commonly EPS (the white beadboard), XPS (the pink or blue boards), or polyisocyanurate. Higher R-value per inch than batts or loose fill. One important caveat: polyiso’s rated R-value (R-5.6 to R-6.5 per inch) is measured at 75°F and drops significantly in cold temperatures. In climate zones 5 and above, derate polyiso to approximately R-4.5 per inch for whole-assembly calculations, or use XPS or EPS instead.
Best for: Basement walls, exterior continuous insulation, under slabs, and cathedral ceilings where cavity depth is limited.
Weakness: Requires accurate cutting and seam-taping for air sealing. Exposed foam board in living spaces must be covered with fire-rated drywall (typically half-inch) by code.
Mineral wool (rock wool / slag wool)
Made from volcanic rock or steel slag, spun into fibers. Sold under brands like Rockwool. Similar format to fiberglass batts but denser, fire-resistant to extremely high temperatures, more water-resistant, and better at sound dampening.
Best for: Fire-separation walls, exterior walls where moisture resistance matters, soundproofing between floors.
Weakness: More expensive than fiberglass batts and not always available at every retailer. Confirm stock before specifying.
Where each type belongs: application map
Most guides organize insulation by material type. This table does it by location instead, which is how an actual decision gets made. Here’s where each of the home insulation types belongs — and what to watch for in each spot.
| Location | Best type(s) | Notes |
|---|---|---|
| Attic floor (open attic) | Blown-in cellulose or fiberglass; fiberglass batts | Easiest DIY location. Blown-in covers irregularities better. Air seal penetrations first. |
| Attic roof deck (conditioned attic) | Closed-cell spray foam; rigid foam board | Higher cost. Only needed if using attic as living space. |
| Exterior walls (new construction) | Fiberglass batts; mineral wool batts; dense-pack cellulose | Batts are standard. Mineral wool adds fire and moisture resistance. |
| Existing walls (retrofit) | Dense-pack cellulose (blown into wall cavity) | Requires drilling holes or removing siding/drywall. Pro job. |
| Crawl space walls | Closed-cell spray foam; rigid foam board | Spray foam earns its cost here — irregular surfaces, moisture risk, and closed-cell doubles as a vapor barrier. Full encapsulated crawl space approach. |
| Rim joists | Closed-cell spray foam; rigid foam board + caulk | Classic spray foam application — small area, high air leakage, hard to batt-insulate properly. |
| Basement walls | Rigid foam board; closed-cell spray foam | Address moisture before insulating. Rigid board is cost-effective here. |
| Floors over garage or unheated space | Fiberglass batts; rigid foam board | Batts fit between floor joists but need to be held up — they can fall out without support. |
R-value explained: what number do you actually need?
R-value measures thermal resistance. R-30 resists heat transfer twice as well as R-15. Every inch of insulation material adds to the total R-value, so four inches of R-3.5-per-inch cellulose gives you R-14.
The Department of Energy divides the U.S. into climate zones 1 through 7, from South Florida (zone 1, warmest) to northern Minnesota and Alaska (zones 6 to 7, coldest). Required R-values scale with zone: colder climates need higher numbers to offset greater temperature differences.
DOE recommended R-values by zone and location
| Climate Zone | Representative States / Areas | Attic (uninsulated) | Attic (adding to existing) | Floors | Walls (cavity) |
|---|---|---|---|---|---|
| Zone 1–2 | FL, HI, Southern TX, Southern LA | R-30 to R-49 | R-38 | R-13 | R-13 to R-15 |
| Zone 3 | TX, GA, SC, most of CA | R-30 to R-60 | R-38 | R-19 to R-25 | R-13 to R-15 |
| Zone 4 | VA, KY, TN, OH, most of MD, OR, WA | R-38 to R-60 | R-49 | R-25 to R-30 | R-13 to R-21 |
| Zone 5 | MI, WI, MN, IL, IN, CO (Denver), NY, southern New England | R-49 to R-60 | R-49 | R-25 to R-30 | R-13 to R-21 |
| Zone 6–7 | Northern MN, ND, MT, ID, northern ME, most of AK | R-49 to R-60 | R-60 | R-25 to R-30 | R-15 to R-21 |
To find your exact climate zone, check the DOE or ENERGY STAR climate zone map and enter your ZIP code at energystar.gov. Most homeowners in the continental U.S. fall in zones 3 to 5.
R-value recommendations based on DOE guidance aligned with 2021 IECC (the most widely adopted code version as of 2025–2026). Local codes may vary — check with your county building department or energystar.gov for jurisdiction-specific requirements.
How much existing insulation do you have?
Before adding anything, it’s worth knowing your starting point. In an accessible attic, use a ruler or tape measure. If your existing insulation is compressed, damaged, wet, or moldy, address that before adding on top. Adding R-30 of new cellulose on top of R-11 of existing fiberglass gets you approximately R-41 total, not R-30.
How much does home insulation cost?
Costs below are national averages for professional installation as of early 2026. DIY material-only costs run roughly 40 to 60 percent lower for types where DIY is feasible. All figures assume a standard accessible attic of approximately 1,000 to 1,500 sq ft.
| Insulation Type | R-value per inch | Installed cost (per sq ft) | Installed cost (1,500 sq ft attic) | DIY material cost (1,500 sq ft) | DIY feasible? |
|---|---|---|---|---|---|
| Fiberglass batts | 3.1–3.4 | $1.00–$2.00 | $1,500–$3,000 | $600–$1,200 | Yes |
| Blown-in fiberglass | 2.2–2.7 | $1.00–$2.00 | $1,500–$3,000 | $500–$1,000 | Yes (blower rental) |
| Blown-in cellulose | 3.5–3.8 | $1.50–$3.00 | $2,200–$4,500 | $600–$1,200 | Yes (blower rental) |
| Mineral wool batts | 3.7–4.2 | $2.00–$4.00 | $3,000–$6,000 | $1,400–$2,500 | Yes |
| Open-cell spray foam | 3.5–3.8 | $1.50–$3.50 | $2,200–$5,200 | Not recommended | No |
| Closed-cell spray foam | 6.0–7.0 | $4.00–$8.00 | $6,000–$12,000 | Not recommended | No |
| Rigid foam board (XPS) | 5.0 | $1.50–$3.50 | $2,200–$5,200 | $1,200–$2,500 | Yes (walls/basement) |
Costs vary by region. Labor rates are 20 to 40 percent higher in coastal metros than the Midwest, and vary further depending on existing conditions and the scope of air sealing included. Always get at least two quotes and ask each contractor to itemize labor, materials, and air sealing separately.
Attic Insulation Savings Calculator
Enter your attic size and current R-value to estimate costs and annual savings.
Spray foam vs. fiberglass insulation: the real money comparison
This is the comparison most homeowners are actually trying to make. The spray foam vs fiberglass insulation debate gets framed as a premium vs. budget choice — but that framing misses the point. Here’s what the numbers actually show.
Where spray foam genuinely wins
Closed-cell spray foam has two real advantages over fiberglass in specific applications: R-value per inch (6 to 7 versus 3.1 to 3.4) and simultaneous air sealing. In locations where cavity depth is limited, a 2-inch rim joist, a shallow cathedral ceiling, a crawl space with irregular block walls, those two factors matter. You can’t fit enough fiberglass into a 3.5-inch rim joist cavity to reach R-20. Spray foam gets you there.
Open-cell spray foam (the less dense, cheaper version) doesn’t have the R-value advantage. Its R-value per inch is similar to fiberglass. Its main use case is interior walls for sound control and hard-to-reach spaces where batts won’t stay.
Where fiberglass or cellulose wins on ROI
For a standard open attic with adequate joist depth, fiberglass batts or blown-in cellulose almost always deliver better return on investment. Using DOE savings estimates and representative 2026 installer pricing, the result is consistent: for a standard open attic, closed-cell spray foam does not come close to paying back against blown-in cellulose. The thermal performance at equal R-values is the same. The cost is not.
| Blown-in cellulose | Closed-cell spray foam | |
|---|---|---|
| Installed cost (1,500 sq ft attic, to R-49) | ~$2,500–$4,000 | ~$10,000–$15,000 |
| Annual energy savings (DOE estimate, avg U.S. home) | $300–$600/yr | $300–$600/yr* |
| Payback period | 5–10 years | 20–40+ years |
| 10-year net savings | +$500–$3,500 | Negative to breakeven in most scenarios |
*Same savings range because at the same total R-value, annual energy savings are the same. You’re not saving more money per year with spray foam in an open attic. You’re paying more upfront for the same thermal result.
The air sealing factor
In an older home, air leakage often accounts for 25 to 40 percent of heating and cooling energy loss. This is where spray foam’s “insulate and air-seal in one step” pitch has real merit in concept. The practical question is whether it’s the most cost-effective way to achieve that air sealing. In an open attic, DIY air sealing before blown-in insulation is almost always more economical. In a crawl space or at rim joists, spray foam often is the right call.
Can you DIY? A realistic guide by type
DIY insulation can save 40 to 60 percent of installed cost. Here’s the realistic breakdown.
Genuinely DIY-friendly
Fiberglass batts (attic floor, floor joists): Cut to fit, press in place. Wear a respirator, safety glasses, and long sleeves — fiberglass fibers irritate skin and lungs. Knee pads help for attic work. This is the most beginner-accessible insulation project.
Worth having before you start: 3M half-face respirator with P100 filters — fiberglass fibers are a real lung irritant; this is the right protection for attic work.
Blown-in cellulose (attic floor): Rent a blowing machine from Home Depot or Lowe’s — typically free with the purchase of 10 or more bags of insulation. You’ll need a helper. More physical than batts, but cellulose achieves better coverage over irregular surfaces. Before you start, stake depth markers every few feet so you can verify you’ve hit your target R-value as you go — otherwise it’s easy to under-insulate without realizing it.
Do this before you blow: attic insulation depth markers — cheap insurance against under-insulating, tells you exactly when you’ve hit your R-value target.
Mineral wool batts (walls, between floors): Cuts easily with a serrated knife, doesn’t itch like fiberglass, and holds its shape in cavities. A bit pricier than fiberglass but easier to work with for most people.
Doable with prep work
Rigid foam board (basement walls, exterior): Measuring and cutting accurately matters here. Seams need the right tape (foil-faced tape for polyiso, compatible tape for XPS). Exposed foam board in living spaces must be covered with fire-rated material such as half-inch drywall. A capable DIYer can handle this with some planning.
Hire a pro
Spray foam (any type, large areas): Two-component kits exist for small DIY applications like rim joists and gap filling, but a full attic or crawl space job requires professional equipment, training, and safety protocols. Improperly mixed spray foam off-gasses for far longer than correctly applied professional foam. If you’re using spray foam for small gaps, plan to vacate the space for at least 24 to 48 hours.
Dense-pack wall insulation (retrofit): Requires drilling into walls, specialized blowing equipment, and experience reading fill density. This is a pro job without exception.
Does insulation actually reduce energy bills?
Yes, with a realistic expectation about how much. The Department of Energy estimates that adding insulation to an under-insulated home can reduce heating and cooling costs by 10 to 20 percent. The actual number depends on how far below code your current insulation is, your local climate, your heating and cooling system, and how much air sealing is done alongside the insulation work. We’ve seen homeowners in older drafty homes hit the high end of that range; well-sealed newer homes tend to see more modest gains. Your specific number will depend on factors a calculator can’t fully account for.
10-year cost and savings: upgrading to R-49 (1,500 sq ft attic)
Here’s how that plays out in dollar terms. These figures use a conservative $400/year savings estimate — homes with worse starting conditions will do better, and the math shifts further in favor of DIY options.
Assumptions: 1,500 sq ft attic, upgrading from approximately R-11 (common in homes built before 1990) to R-49. Average U.S. energy cost of $0.16/kWh. Annual savings estimate of $400/year (conservative midpoint of DOE range). Professional installation costs.
| Insulation Type | Installed Cost | Annual Savings (est.) | Payback Period | 10-Year Net Savings | Best For |
|---|---|---|---|---|---|
| Blown-in cellulose | $2,500–$4,000 | $300–$600/yr | 5–10 years | +$500–$1,500 | Attic retrofits, best overall ROI hired out |
| Fiberglass batts (DIY) | $600–$1,200 | $300–$600/yr | 1–3 years | +$2,800–$5,400 | Open attics, budget-conscious, capable DIYers |
| Fiberglass batts (pro) | $1,500–$3,000 | $300–$600/yr | 4–8 years | +$1,000–$2,500 | Standard attic upgrades, hired installation |
| Mineral wool batts | $3,000–$5,000 | $300–$600/yr | 6–12 years | $0–$1,000 | Fire-risk areas, moisture-prone attics |
| Closed-cell spray foam | $8,000–$15,000 | $300–$600/yr | 15–40+ years | Negative to breakeven in most scenarios | Tight cavities, crawl spaces. Not standard attics. |
The DIY fiberglass row stands out for a reason: a weekend in an attic is the highest-ROI insulation upgrade available to most homeowners. Professional blown-in cellulose is the best ROI option when hiring out.
Air sealing: the step most contractors underbid
Air sealing and insulation are separate jobs that are best done together. Insulation slows conductive heat transfer. Air sealing stops convective heat loss through gaps — and in older homes, those gaps often account for more energy loss than thin insulation does. The primary targets in an attic:
- Attic hatch or pull-down stairs — often uninsulated and unsealed, a major source of heat loss
- Recessed light fixtures — gaps around the housing can be significant, especially in older can lights
- Pipe and wire penetrations — every hole through the top plate is a direct air path
- Duct boots and HVAC chases — gaps between duct connections and the ceiling drywall
All of these can be addressed with canned spray foam, caulk, and rigid foam board for $50 to $200 in materials — before a single bag of blown-in insulation goes down. Ask any contractor for an itemized air sealing scope; if they can’t provide one, that’s a red flag.
The go-to for attic air sealing: Great Stuff Pro gaps & cracks foam — what contractors reach for on pipe penetrations, top plates, and light fixture gaps before insulating.
How to choose: a decision framework by situation
Rather than recommending one type universally, here’s how to navigate the main home insulation types by situation. Among all options for standard attic retrofits, blown-in cellulose typically offers the best ROI when hiring out — best overall coverage, widely available, and cost-effective. If you’re not sure where your home’s biggest heat loss is occurring, a home energy audit is the most useful first step — it typically costs $200 to $600 and tells you exactly where to invest before you spend a dollar on materials.
Before getting any quotes, check what rebates are available: the federal Energy Efficient Home Improvement Credit covers up to 30% of insulation material costs (capped at $1,200/yr), and many utilities and states layer additional rebates on top. Search your utility name + “insulation rebate” or visit dsireusa.org for your state.
If you’re hiring out any insulation job, here’s what every good quote should include:
- Starting R-value — what’s already in the attic (requires them to measure, not guess)
- Target R-value — the number you’re reaching, with the zone and code basis stated
- Air sealing scope — specifically what penetrations will be sealed and at what cost
- Material and labor itemized separately — so you can compare bids apples-to-apples
- Installed depth in inches — for blown-in material, this should be clearly stated, not just “to R-49”
Any contractor who won’t provide this information upfront is worth skipping. As a rough sanity check: blown-in cellulose or fiberglass should come in at $1.50 to $3.00 per sq ft installed for a standard accessible attic. Quotes meaningfully above that range deserve an itemized explanation.
→ Home Energy Audit: What It Is and Is It Worth It — our complete guide
| Your situation | Recommended approach |
|---|---|
| Open attic, adding on top of existing, comfortable with a weekend project | DIY fiberglass batts or blown-in cellulose. Air seal penetrations first. Highest ROI scenario. |
| Open attic, want to hire it out, budget is the primary concern | Get quotes for blown-in cellulose or fiberglass. Specify R-49 for most zones. Ask what air sealing is included. |
| Rim joists and band joists are uninsulated | Closed-cell spray foam is the right call here. Small area, legitimate spray foam application. Get a targeted quote for this specifically. |
| Crawl space with uninsulated walls, moisture issues | Address moisture first (vapor barrier, drainage). Then closed-cell spray foam on walls or rigid foam board. Pro job. |
| New construction or gut renovation, choosing wall insulation | Fiberglass or mineral wool batts for standard framing. Dense-pack cellulose is a premium option for better air resistance. Spray foam in walls is rarely justified. |
| Older home, whole-house comfort issue, not sure where to start | Start with a home energy audit. A blower door test will identify where your actual air leakage is, which often points to the attic hatch, recessed lights, and wall-to-ceiling connections before bulk insulation is even needed. |
Frequently Asked Questions
Conclusion
Choosing among home insulation types comes down to where in your house, what R-value your climate zone requires, and whether the project is DIY or hired out. For most standard attic upgrades, fiberglass batts or blown-in cellulose deliver the best return on investment. Spray foam earns its cost premium in tight cavities, crawl spaces, and rim joists, not in open attics. Get the R-value right, air-seal before you insulate, and you’ll make a better decision than most homeowners who took a contractor’s word for it. If you’re not sure where your home’s biggest heat loss is, start with our home energy audit guide before spending money on materials.
Better insulation also changes the math on heat pump sizing — see our heat pump home guide for how the two upgrades work together.
Affiliate disclosure: Acara Institute participates in the Amazon Associates program. Links marked #ad earn us a small commission if you make a purchase, at no extra cost to you. This does not influence our recommendations. We have no financial relationship with any insulation installer, contractor, or manufacturer. Not professional advice: Cost and savings figures are national averages based on DOE data and 2026 market pricing. Your actual costs and savings will vary. Always obtain multiple quotes from licensed contractors before undertaking any insulation project.